Absorbent core comprising a high loft central layer and channels

ABSTRACT

An absorbent core for use in an absorbent article, the absorbent core extending in a transversal direction and a longitudinal direction. The absorbent core includes a fluid-permeable top layer, a bottom layer, and a central layer between the top layer and the bottom layer. The central layer may be a high loft fibrous nonwoven layer, in particular having a density of less than about 0.200 g/cc, measured at a pressure of 4.14 kPa. Superabsorbent polymer particles may be blended with the fibers of the central layer, except for one or more longitudinally-extending channels substantially free of superabsorbent polymer particles.

FIELD

The invention relates to absorbent cores for use in personal hygieneabsorbent articles. The absorbent cores may be in particular be used inbaby diapers or training pants.

BACKGROUND

Absorbent articles for personal hygiene such as disposable baby diapers,training pants for toddlers or adult incontinence undergarments, aredesigned to absorb and contain body exudates, in particular urine. Theseabsorbent articles comprise several layers providing differentfunctions, typically including a topsheet, a backsheet and in-between anabsorbent core, among other layers.

The absorbent core should be able to absorb and retain the exudates fora prolonged amount of time, for example overnight for a diaper, minimizere-wet to keep the wearer dry, and avoid soiling of clothes or bedsheets. The majority of currently marketed absorbent cores comprise asabsorbent material a blend of comminuted wood pulp cellulose fibers withsuperabsorbent polymers (SAP) particles, also called absorbent gellingmaterials (AGM).

Absorbent cores without cellulose fibers (also called “airfelt-free”cores) have also been proposed. The SAP particles may be for exampleenclosed within discrete pockets formed between two substrates, or theSAP particles may be adhesively attached to a core wrap by an adhesive.Absorbent structures that comprise superabsorbent polymers, optionally acellulosic material, and at least a pair of substantially longitudinallyextending absorbent material free zones that can form channels as theabsorbent structure absorb a fluid have also been disclosed. Other typesof airfelt-free cores have been disclosed. Typically airfelt-free coresrequire high permeability SAP to perform optimally because there are nocellulose fibers to draw the fluid by capillarity within the core. Highpermeability SAP may however have a lower absorbent capacity and be morecostly than conventional SAP used in airfelt core.

While the previously proposed absorbent cores can provide goodabsorbency capacity, there is a continuous need to improve theproperties of cores in a cost effective manner. In particular there is acontinuous need to improve wearing comfort, increase production speedand reduce raw material usage while keeping optimal fluid managementproperties.

SUMMARY

The present invention is directed to an absorbent core extending in atransversal direction and a longitudinal direction, and comprising afluid-permeable top layer, a bottom layer, and a central layersandwiched between the top layer and the bottom layer. The central layeris a high loft fibrous nonwoven layer having a front edge, a back edgeand two longitudinally extending side edges. The central layer comprisessuperabsorbent polymer particles blended with the fibers of the centrallayer and, as seen from above the plane formed by the transversal andlongitudinal directions, one, two or more longitudinally-extendingchannel zones (herein referred to as “channels”), which aresubstantially free of superabsorbent polymer particles. The channels maybe spaced away from the two longitudinally extending side edges.

The high loft central layer may be free of cellulose fibers, and moregenerally the whole of the absorbent core may be free of cellulosefibers. The absorbent cores can however use SAP materials similar tothose used in cellulose fibers containing cores. In particular the SAPparticles used may have a permeability at equilibrium expressed as UPM(Urine Permeability Measurement) value of less than 30, in particularless than 20, or less than 15, or less than 10 UPM units, where 1 UPMunit is 1×10⁻⁷ (cm³.s)/g. Such low UPM SAP are typically used inconventional airfelt containing absorbent cores. The UPM value ismeasured according to the UPM Test method set out in herein-below in the“test procedure” section. The UPM Test method measures the flowresistance of a pre-swollen layer of superabsorbent polymer particles,i.e. the flow resistance is measured at equilibrium. Therefore, such SAPparticles having a low UPM value exhibit a low permeability when asignificant volume of the absorbent article is already wetted by theliquid exudates. These SAP having a low UPM value are typically cheaperthan higher UPM material, but may be the source of leakage if a largeamount of fluid such as urine is to be absorbed in a short time inairfelt free cores. In the present invention, the high loft of thecentral layer and the channels cooperate to provide fluid passages thatmore efficiently use these SAP having a low UPM values. An insultingfluid may be more efficiently directed through the channels inside thecore, as well as being distributed over the length of the channels tolarger areas of the core, while the void areas of the high loft layeralso provide for an improved fluid passage. When the channels are spacedaway from the longitudinally extending side edges, this further reducesthe risk of side leakage.

In addition, as the SAP swells in the areas outside the channels, thelater will form three-dimensional depressions that, particularly in thecrotch area, may provide zones which can be more easily compressed incross-direction by the thighs of the users. In other words, the channelsmay become bending lines for enhanced fit and comfort when the SAP hasswollen. The top, central and bottom layers may be attached to eachother in the channel zones for example by gluing, mechanical bonding,ultrasonic bonding or heat bonding in the channels to create morepermanent three-dimensional depressions when the SAP swells.

The top layer and the bottom layer may each be a nonwoven material. Lowbasis weight paper, which is readily available and a relatively cheapsubstrate, could also be used as top layer and/or bottom layer. Theabsorbent core may also comprise a wrapping layer that completely coversthe bottom layer and forms a C-wrap around the longitudinally extendingside edges of the central layer to at least partially cover the toplayer. The C-wrap may be formed in the other direction too, i.e.completely covering the top layer and at least partially covering thebottom layer. A wrapping layer can provide an improved control of theSAP thus preventing losses on the side edges of the core.

Each of the channels may be completely surrounded by the rest of thecentral layer comprising SAP particles, or the channels may extend fromthe front edge to back edge of the central layer. The firstconfiguration provides additional benefits in terms of reduced leakagestowards the front and back end of the core. On the other hand, the frontend and back end are typically relatively spaced away from the site ofurine deposition. The second configuration may thus be in generalacceptable, and may be easier to make, as it can be made for examplewith a static shielding frame, as will be discussed further below.

The absorbent cores may comprise a dual layer construction comprising afirst central high loft layer and a second central high loft layer. Thisconstruction may provide additional benefit for example in terms of SAPimmobilization because the SAP particles may be sandwiched between thesetwo layers. The present invention also relates to processes for makingthe absorbent cores of the invention. Various processes may be used,some of which are further disclosed below and in the claims. These andother optional features of the invention will be described in thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of an exemplary absorbent core with the top andcentral layers partially removed and channels extending along the fulllength of the core;

FIG. 2 shows a cross-sectional view of the absorbent core of FIG. 1;

FIG. 3 shows a cross-sectional view of the absorbent core of FIG. 1 witha wrapping layer;

FIG. 4 shows a schematic view of the process for making the absorbentcore of FIG. 1;

FIG. 5 shows an exemplary shielding plate for use in the process of FIG.4;

FIG. 6 shows a top view of an alternative absorbent core wherein thechannels are completely surrounded by a SAP containing zone;

FIG. 7 shows a cross-section of the core of FIG. 6;

FIG. 8 shows a schematic view of the process for making the absorbentcore of FIG. 6, using SAP printing rolls;

FIG. 9 illustrates the surface of a SAP reservoir of a printing rollcomprising two curved raised strips;

FIG. 10 shows a cross-section view of an alternative absorbent corecomprising two central high loft nonwovens;

FIG. 11 shows a schematic view of the process for making the absorbentcore of FIG. 10;

FIG. 12 is a schematic cross-sectional side view of an absorbent articlecomprising the absorbent core of FIG. 10 with a wrapping layer;

FIG. 13 is a partial cross-sectional side view of a suitablepermeability measurement system for conducting the Urine PermeabilityMeasurement Test.

FIG. 14 is a cross-sectional side view of a piston/cylinder assembly foruse in conducting the Urine Permeability Measurement Test.

FIG. 15 is a top view of a piston head suitable for use in thepiston/cylinder assembly shown in FIG. 14.

FIG. 16 is a cross-sectional side view of the piston/cylinder assemblyof FIG. 14 placed on fritted disc for the swelling phase.

DETAILED DESCRIPTION Introduction

As used herein, the terms “comprise(s)” and “comprising” are open-ended;each specifies the presence of the feature that follows, e.g. acomponent, but does not preclude the presence of other features, e.g.elements, steps, components known in the art or disclosed herein. Theseterms based on the verb “comprise” should be read as encompassing thenarrower terms “consisting essentially of” which excludes any element,step or ingredient not mentioned which materially affect the way thefeature performs its function, and the term “consisting of” whichexcludes any element, step, or ingredient not specified. Any preferredor exemplary embodiments described below are not limiting the scope ofthe claims, unless specifically indicated to do so. The words“typically”, “normally”, “preferably”, “advantageously”, “in particular”and the likes also qualify features which are not intended to limit thescope of the claims unless specifically indicated to do so.

As used herein, the terms “nonwoven layer” or “nonwoven web” are used inthe general meaning of a manufactured sheet, web or batt ofdirectionally or randomly orientated fibers, bonded by friction, and/orcohesion and/or adhesion, excluding paper and products which are woven,knitted, tufted, stitch-bonded incorporating binding yarns or filaments,or felted by wet-milling, whether or not additionally needled. Thefibers may be of natural or synthetic origin and may be staple orcontinuous filaments or be formed in situ. Commercially available fibershave diameters ranging from less than about 0.001 mm to more than about0.2 mm and they come in several different forms such as short fibers(known as staple, or chopped), continuous single fibers (filaments ormonofilaments), untwisted bundles of continuous filaments (tow), andtwisted bundles of continuous filaments (yam). Nonwoven webs can beformed by many processes such as meltblowing, spunbonding, solventspinning, electrospinning, carding and airlaying. The basis weight ofnonwoven webs is usually expressed in grams per square meter (g/m² orgsm).

General Description of the Absorbent Core

As used herein, the term “absorbent core” refers to an individualcomponent, which is placed, or is intended to be placed, within anabsorbent article and which comprises an absorbent material. Theabsorbent core is typically the component of an absorbent article thathas the most absorbent capacity of all the components of the absorbentarticle and which comprises all, or at least the majority of,superabsorbent polymer (herein referred to as “SAP”) particles. Theterms “absorbent core” and “core” are herein used interchangeably.

The absorbent cores of the invention are substantially planar. Bysubstantially planar, it is meant that the absorbent core can be laidflat on a planar surface. The absorbent cores may also be typically thinand conformable, so that they can also be laid on a curved surface forexample a drum during the making process, or stored and handled as acontinuous roll of stock material comprising a plurality of cores beforebeing converted into an absorbent article.

For ease of discussion, the exemplarily absorbent cores of FIG. 1 andFIG. 6 are represented in a flat state. The absorbent core is relativelythin relative to its other dimensions in the transversal direction (x)and the longitudinal direction (y). Unless otherwise indicated,dimensions and areas disclosed herein apply to the core in this flat-outconfiguration. The absorbent article may be notionally divided by alongitudinal axis (also called longitudinal centerline, not shown in theFigures) extending from the front edge to the back edge of the core anddividing the core in two substantially symmetrical halves relative tothis axis, when the core is placed flat and viewed from above as in FIG.1 for example.

For ease of discussion, the absorbent cores, articles and processes ofthe invention will be discussed with reference to the Figures and thenumerals referred to in these Figures; however these are not intended tolimit the scope of the claims unless specifically indicated.

Central Layer

The absorbent cores of the invention comprise a central layer 43, asfirst illustrated in FIGS. 1-2. The central layer 43 is a high loftnonwoven fibrous layer. The term “high loft” refers to low density bulkyfabrics, as compared to flat, paper-like fabrics. High loft webs arecharacterized by a relatively low density. This means that there is arelatively high amount of void space between the fibers in which thesuperabsorbent particles can be blended in. The high loft nonwovenfibrous layer (without the superabsorbent material) of the invention maytypically have a density below 0.200 g/cc, in particular ranging from0.015 g/cc to 0.150 g/cc, in particular from 0.030 g/cc to 0.100 g/cc,for example 0.065 g/cc. The density can be calculated by dividing thebasis weight of the high loft layer by its thickness measured at apressure of 4.14 kPa (see the method details further below in the “testprocedure” section).

The high loft nonwoven layer may advantageously be a spunmelt nonwoven.Spunmelt is a generic term describing the manufacturing of nonwoven websdirectly from thermoplastic polymers. It encompasses 2 processes and thecombination of both: spunlaid (also known as spunbond) nonwoven andmeltblown nonwoven. In a spunlaid process, polymer granules are meltedand molten polymer is extruded through spinnerets. The continuousfilaments are cooled and deposited on to a conveyor to form a uniformweb. Some remaining temperature can cause filaments to adhere to oneanother, but this cannot be regarded as the principal method of bonding.The spunlaid process has the advantage of giving nonwovens greaterstrength, but raw material flexibility is more restricted. Co-extrusionof second components is used in several spunlaid processes, usually toprovide extra properties or bonding capabilities. In meltblown webformation, low viscosity polymers are extruded into a high velocityairstream on leaving the spinneret. This scatters the melt, solidifiesit and breaks it up into a fibrous web. Illustrations of these processesare for example provided on the Edana website:http://www.edana.org/discover-nonwovens/how-they're-made/formation.

The fibers forming the central layer may be made partially or entirelyof a relatively resilient synthetic fibers, in particular polypropylene(PP), polyamide (PA, such as nylons) or polyethylene terephthalate (PET)fibers. The diameter of the fibers may for example range from 0.01 mm to0.50 mm.

Typically the central layer will be homogenous in both transversaldirection and longitudinal direction, especially regarding itsthickness, basis weight and density. The high loft nonwoven layer may inparticular have a thickness ranging from 0.30 mm to 2.00 mm, for example1.0 mm as measured at a pressure of 4.14 kPa (according to the testmethod described further below). The basis weight of the high loftcentral layer may for example range from 15 gsm to 500 gsm, inparticular from 30 gsm to 200 gsm, for example 64 gsm. The valuesindicated herein for the central layer are considered for the high loftnonwoven material taken in isolation, that is before the SAP particleshave been blended between the fibers of an adhesive applied to it. Whenthe absorbent core comprises two or more high loft central layers, aswill be discussed further below, these ranges for the thickness andbasis weight may be the same for each layer, or may be divided by thenumber of central high loft layers. For example, the absorbent core cancomprise two high loft central layers as illustrated in FIG. 10 made ofPET fibers and each having a thickness of ca. 0.50 mm, a basis weight ofca. 32 gsm and a density of ca. 0.065 g/cc.

The central layer 43 has a front edge 280, a back edge 282 and twolongitudinally-extending side edges 284, 286. The front and back edgesare typically shorter than the side edges. The front edge of the centrallayer corresponds to the edge intended to be placed towards the frontedge of the absorbent article in which the core is or will beintegrated. The superabsorbent material may be distributed in higheramount towards the front half of the central layer relative to the backhalf of the central layer. This is because there is typically more fluiddischarged towards the front of the article in which a core will beincorporated. In addition to the profiled SAP distribution in thelongitudinal direction (y), the SAP may be also be profiled in thetransversal direction (x). Of course, the SAP may be also homogenouslydistributed in the transversal (x) and the longitudinal direction (y),which simplifies production: in that case any of the two shorter sidesmay be considered as the front edge and the opposite side will be theback edge. The absorbent cores may comprise one, two or more such highloft central layer. An absorbent core comprising two high loft centrallayers is discussed further below.

The central layer (or layers) serves as substrate for the SAP particles60 which are blended between its fibers in at least one SAP containingzone 27. The central layer further comprises at least one longitudinallyextending channel substantially free of SAP particles. This will bedetailed further below. The SAP particles may be substantially uniformlyblended across the thickness of the high loft nonwoven, but it is notexcluded that the SAP particles may be more present on one side of thehigh loft nonwoven than the other, for example depending on the processof fabrication used.

Superabsorbent Material Particles

The central layer comprises a superabsorbent polymer (herein abbreviatedas “SAP”) in the form of particles 60 blended within the fibers of thehigh loft nonwoven layer. Any conventional SAP materials may be used.Typical SAP includes a variety of water-insoluble, but water-swellablepolymers capable of absorbing large quantities of fluids. The term“superabsorbent polymer” refers herein to absorbent materials, which maybe cross-linked polymeric materials, and that can absorb at least 10times their weight of an aqueous 0.9% saline solution as measured usingthe Centrifuge Retention Capacity (CRC) test (EDANA method WSP241.2-05E). The SAP may in particular have a CRC value of more than 10g/g, or more than 20 g/g, or of from 20 g/g to 50 g/g, or from 25 g/g to45 g/g.

The superabsorbent polymers are in particulate form so as to be flowablein the dry state and thus easily deposited on the substrate. Typicalparticulate absorbent polymer materials are made of poly(meth)acrylicacid polymers. However, it is not excluded that other polymer materialsmay also be used. The SAP particles may be relatively small (under 1 mmin their longest dimension) in their dry state and may be roughlycircular in shape, but granules, fibers, flakes, spheres, powders,platelets and other shapes and forms are also known to persons skilledin the art. Typically, the SAP may be in the form of spherical-likeparticles.

As indicated previously, one advantage of the invention is that SAPparticles having a relatively low permeability at equilibrium (UPMvalue) may be used. These particles are typically used in airfeltcontaining core because the cellulose fibers generally increase thepermeability of the absorbent material. Airfelt free absorbent cores onthe other hand typically require high permeability SAP to performoptimally. High permeability SAPs however are typically more costly thanlow permeability SAPs. The superabsorbent polymer particles used in theinvention may thus have a UMP of below 30×10⁻⁷ cm³.s/g, in particularbelow 25×10⁻⁷ cm³.s/g, in particular below 20×10⁻⁷ cm³.s/g, inparticular below 15×10⁻⁷ cm³.s/g, in particular from 1×10⁻⁷ cm³.s/g to10×10⁻⁷ cm³.s/g as measured by the Urine Permeability Measurement Testindicated below in the “Test Procedure” section. The Urine PermeabilityMeasurement Test has been originally disclosed in PCT applicationWO2012/174026A1.

Although it is not excluded that the absorbent core may comprisecellulose fibers, the absorbent core may in particular comprise no oronly small amount of cellulose fibers, such as less than 20%, inparticular less than 10%, 5% or even 0% of cellulose fibers by weight ofthe absorbent core. The absorbent material may thus consist or consistessentially of SAP. For the purpose of determining the amount ofcellulose fibers in the absorbent core, any paper or tissue paper layerserving as top layer, bottom layer or wrapping layer are disregarded.

Channel

The central layer 43 comprises at least one (in particular one, two ormore) longitudinally-extending zones 26 substantially free of SAPparticles 60. These zones are considered, as seen as in FIGS. 1 and 6,from above in the plane formed by the transversal and longitudinaldirections. These one or more zones substantially free of SAP particlesare referred to herein as “channels”. For convenience, the plural formwill be used even if there is only one of these zones. The rest of thecentral layer outside the channels 26 defines at least one zone 27having superabsorbent polymer particles 60.

By “substantially free of SAP”, it is meant that the basis weight of theSAP material in each of these zones is at least less than 25%, inparticular less than 20%, in particular less than 10%, of the averagebasis weight of the SAP in the central layer as a whole. The channelsmay in particular be zones of the central layer where there are no SAPparticles. In this regard, minimal amount such as involuntarycontaminations with SAP particles that may occur during the makingprocess are not considered as absorbent material.

The channels extend longitudinally in the central layer. By“longitudinally extending”, it is meant that the channels extend more inthe longitudinal direction (y) than in the transversal direction (x).The channels may for example have a length (projected on an axisparallel to the longitudinal direction) which is at least 5%, inparticular from 10% to 70%, or from 15% to 60% of the length of thecentral layer. The channels 26 may be oriented parallel to thelongitudinal direction, as shown in FIG. 1. However it is not excludedthat the channels may be curved, in particular concave towards thelongitudinal axis—as in inverted brackets:) (as indirectly shown on FIG.9—or straight and tilted at an angle relative to the longitudinaldirection. The channels may be advantageously spaced away from thelongitudinally extending side edges 284, 286 of the central layer. Inthis way, the SAP particles along the longitudinal side edges provide abarrier for the fluid in the channels before it reaches the side edgesof the central layer. The channels 26 may be for example spaced at adistance of at least 5 mm from the side edges of the central layer. Thecentral layer may comprise at least two channels placed symmetrically oneach side of the longitudinal centerline, as illustrated by the channels26 in FIG. 1 and FIG. 6. There may be of course only one channel, oralternatively more than two channels, for example three channels, or twopairs of channels, present. Advantageously the channels aresymmetrically disposed relative to the longitudinal axis of the core.

The channels may extend along the whole length of the central layer 43,thus extending from the front edge 280 of the central layer to theopposed back edge 282. This is illustrated in FIG. 1 for example. On theother hand, it is also considered that the channels may also be spacedaway (for example at least by 5 mm) from the front edge and/or back edgeof the central layer. This is illustrated in FIG. 6, and in thisconfiguration the channels are entirely surrounded by the SAP particlespresent in the rest of the central layer. This provides an additionalleakage barrier at the front and back edges of the central layer. Thechannels extending up to the front and back edges of the central layermay be on the other hand easier to make. Channels extending to the sideedges of the core 284 and 286 (not represented) may on the other hand bebeneficial for example to provide better comfort between the legs of thewearer of the absorbent article.

Bottom Layer and Top Layer

The central layer is sandwiched between a top layer 41 and a bottomlayer 42. The top layer is on the side of the core intended to be placedclosest to the wearer-facing side of the absorbent article. The toplayer is thus liquid-permeable, so that a fluid can easily reach thecentral layer through the top layer during use. The bottom layer ispositioned on the other side of the central layer. It may beliquid-permeable or liquid impermeable. The top layer and the bottomlayer provide a cover on both sides of the central layer for preventingthe SAP particles from falling out of the high loft during the core andarticle making process as well as during use of the absorbent article.

The top and bottom layers may be made of a relatively thin and cheapmaterial, as are commonly used for the production of conventional cores.The top and bottom layers may be for example a tissue paper (airfelt orwetlaid) having a basis weight ranging for example from 5 to 100 gsm, inparticular 10 to 40 gsm. The top and bottom layers may also be formedfrom a low basis weight nonwoven web having a basis weight of between 5gsm and 30 gsm, such as a carded nonwoven, spunbond nonwoven (“S”) ormeltblown nonwoven (“M”), and laminates of any of these. For examplespunmelt polypropylene nonwovens are suitable, in particular thosehaving a laminate web SMS, or SMMS, or SSMMS, structure, and having abasis weight range of about 5 gsm to 20 gsm. Such materials are forexample disclosed in U.S. Pat. No. 7,744,576, US 2011/0268932 A1, US2011/0319848 A1 and US 2011/0250413 A1. Nonwovens materials aretypically inherently hydrophobic, and the top layer may thus be treatedto render it hydrophilic, for example by treating it with a surfactantor other methods as is known in the art. The top layer and the bottomlayer may be made of the same or different material, optionally with thetop layer or bottom layer treated differently to render to the top layermore hydrophilic than the bottom layer.

In addition to the top layer and the bottom layer, the absorbent corecan further comprise a wrapping layer 3 forming a C-wrap around thelongitudinally extending side edges 284, 286 of the core, as shown inFIG. 3. By “C-wrap”, it is meant that the layer covers at least the topside or bottom side of the core, extends along its side edges to formflaps that are then folded and attached, typically by gluing, over theopposite side of the core. The wrapping layer 3 may thus have across-section similar to the letter C (when rotated 90°). A C-wrapconstruction may further help containing the SAP particles during themaking or wearing of the absorbent article. The wrapping layer may forexample be made of a low basis weight nonwoven layer, for example havinga basis weight of from 5 to 40 gsm, in particular from 8 to 25 gsm, inparticular a SMS nonwoven, but other materials are of course possible.The wrapping layer 3 has been represented in FIG. 3 as extending fromthe bottom side of the core and having flaps folded over the top side ofthe core. The inverted configuration is also possible, with theC-wrapped layer 3 extending from the top side and with the flaps foldedover the bottom side. The folded flaps may end and be attached in thevicinity of the longitudinally extending side edges of the core or maybe longer than represented to that they overlap and attached to another.It is also considered that a C-wrap construction may be formed by one ofthe top layer or bottom layer extending transversally along thelongitudinally extending side edges of the core and forming flaps asdescribed for the wrapping layer 3. The presence of a wrapping layer isoptional.

The top layer 41 and/or the bottom layer 42 may be attached to thecentral layer 43. A layer of glue 71 may be for example applied betweenthe top layer and the central layer 43. Any type of conventional glueand glue application method may be used. Typically a hot melt glue maybe uniformly sprayed on the substantially the whole of the surface ofthe layers before putting the two layers in close contact so that theybecome attached. The glue may also be applied by a contact method to oneof the layers, in this case in particular the top or bottom layer,typically by slot-coating a series of parallel thin lines of glue in themachine direction (y direction). A layer of glue 72 may also besimilarly applied between the bottom layer 42 and the central layer 43.

The top layer and/or the bottom layer may also be specifically andadditionally attached to the central layer in the channel zones 26, forexample to maintain the channels relatively free of AGM duringmanufacturing and use of the absorbent article. Such an attachment inthe zones of the channels can be achieved via any known attachment meanssuch as gluing, pressure bonding, ultrasonic bonding, heat bonding orcombination thereof. This further attachment may compress or crimp ofthe central layer in the channels, thus providing three dimensionalchannels already before the core has accepted fluid, which may forexample serve as folding guides for the core.

Process

A continuous process for making the absorbent cores as illustrated inFIG. 1 will now be described with reference to FIG. 4. The variousarrows in FIG. 4 represent the rotational directions of the variousroll-releasing cylinders and roll-winding cylinders and the runningdirections of the manufacturing materials during the production flowprocess. Other processes and modifications are possible and will furtherbe discussed below.

As illustrated in FIG. 4, the apparatus for making the absorbent coresincludes a bottom layer web unwinder 6, a bottom layer glue sprayinghead 7, a high loft central layer web unwinder 8, a first SAP particlessieve plate 9 and vacuum suction box 10, a first pair of hot pressrollers 11 and 12, a second SAP particles sieve plate 13 and vacuumsuction box 14, a top layer web unwinder 15, a top layer spraying head16, second pair of hot press rollers 17 and 18, trimming off knives 19,20, and a product roll winding roller 21. As will be discussed further,a shielding plate 22, illustrated in FIG. 5 is placed between each sieveplates 9, 13 and the central layer 43 to provide that the desiredchannels zones of the central layer remain substantially free of SAPparticles. The vacuum suction box 10 and 14 may also comprise a blindarea (area without vacuum) to reduce SAP deposition in the channelszones.

The first SAP particles sieve plate 9 and the second SAP particles sieveplate 13 may be both provided with a frequency changing and speedadjusting device (not drawn in FIG. 4). The frequency changing and speedadjusting devices of the first and second SAP sieve plates 9, 13 areadjusted to maintain a vibration frequency that matches the product rollwinding roller 21 linear velocity and to ascertain that the sprayedpolymer water absorbing resin (SAP) is mostly uniformly distributed onthe bulky nonwoven fabric 43.

During production, a roll of bottom layer material, for example a paperor nonwoven roll, is installed on the bottom layer web unwinder 6. Ahigh loft nonwoven fabric roll is installed on the central layer webunwinder 8. The SAP particles are charged in the first and second SAPparticles sieve plates 9 and 13. A roll of top layer material, which canbe a paper or nonwoven roll, is installed on the top layer web unwinder15. During the continuous process of making the absorbent cores, thebottom layer 42 passes through the spraying head 7 and is applied on oneside with a glue 72, before being attached to the central layer 43between the first press rollers 11 and 12. The high loft nonwovencentral layer 43 passes through the first SAP particles sieve plate 9and vacuum suction box 10, wherein the SAP particles are deposited intothe central layer and blended into the fibers the central layer from afirst side. The shielding plate 22 and blinded areas, if present, on thesuction box 10 provide that no or a limited amount of SAP is depositedinto the channels zones of the central layer that are intended to remainsubstantially free of SAP particles. It is also possible that the bottomlayer material 6 is first attached to on a first side of the centrallayer 43 before the SAP particles 60 are deposited onto and blendedbetween the fibers of the central layer.

After the bottom layer 42 and the central layer 43 have been attachedbetween the rollers 11 and 12, these combined layers may optionally passbetween a second SAP particles sieve plate 13 and vacuum suction box 14that cooperate to deposit SAP particles onto the second surface of thecentral layer and blend the SAP particles in the fibers of the centrallayer from this second surface. Again, a second shielding plate 22 whichcan be similar to the first shielding plate can be used to provide thatthe desired channels zones 26 of the central layer remain substantiallyfree of SAP particles. The top layer 41 which has been applied with anadhesive 72 by a glue spraying head 16 is then joined to the centrallayer to cover the second surface of the central layer between two pressrollers 17 and 18. Of course in the preceding the top layer and bottomlayer may be used interchangeably.

The press rollers 17 and 18 may have a substantially flat surface, orthey may have elevated areas where extra pressure and heat should beapplied onto the core. These elevated areas may coincide with thechannel areas, and thus provide a mechanical bonding, ultrasonic bondingand/or heat bonding within the channel zones 26. The press rollers11-12, 17-18 may be heated. It is also possible that the rollers haveelevated areas along the longitudinal side edges and/or the back andfront edges (360° perimeter) the core. A better bonding can be achievedin these zones when they are free of SAP as in the channel zones 26.Trimming knives 19 and 20 can be provided to trim the longitudinal sideedges of the continuous band of absorbent core before the stream of theabsorbent core material is finally rolled into a roll of absorbent corematerial by the product roll winding roller 21.

The roll of absorbent core material thus formed may be stored ortransported to an article production site where it is further convertedinto an absorbent product. It is also possible that instead of forming aroll, the stream of absorbent core material may be directly fed into aconverting line, in which case the absorbent cores will beindividualized by cutting along their front and back edges.

A wrapping layer 3 (not represented in FIG. 4) may also be fed beforethe core material is rolled to wrap the top, central and bottom layer asshown discussed in relation to FIG. 3 to prevent losses of SAP thoughthe side edges of the absorbent core. Alternative such wrapping layermay also be attached to the core when further converting the corematerial web.

The process and apparatus discussed above is generally similar to theone disclosed in CN101797201, except for the presence of a staticshielding plate 22 between the sieving plate 9 (respectively 13) on oneside, and the central layer 43 placed on the vacuum suction box 10(respectively 14) on the other side. The shielding plate may be a pieceof metal comprising elongated cut-out zones 23 through which the SAPparticles can flow and with full zones 24 between the cut-out zones 23,as illustrated in FIG. 5. As the central layer (represented by thedashed lines) passes underneath the shielding plate, the SAP particlesare deposited through the cut-out zones 23 and leave the zones of thecentral layer directly situated under the shielding plate substantiallyfree of absorbent material. Also not disclosed in CN101797201 is theoptional usage of patterned pressure rolls 17 and 18 that can providemechanical bonding, ultrasonic bonding and/or heat bonding of the corelayers in the channels.

Instead of a sieving plate/shielding plate system as disclosed in FIG.4, it is also possible to deposit the SAP in the desired areas 27 byusing a plurality of SAP applicators or SAP chutes offset incross-machine direction and working in parallel. The applicators orchutes have a gap between them so that the channel zones between themare not deposited with SAP particles. For example three applicators orchutes having two gaps between them would provide a deposition patternas for the core of FIG. 1. It is also possible to use a SAP printingsystem to apply the SAP on both or one sides of the central layer, sucha SAP printing system is discussed in the next section with reference ofFIG. 8.

Channel Surrounded by a SAP Containing Zone

FIG. 6 illustrates an absorbent core 28 a according to the inventionhaving channels 26 not extending to the front edge 280 and back edge 284of the central high loft layer 43. The channels 26 are therefore fullysurrounded by a zone 27 of the central layer comprising SAP particles.The rest of the absorbent core construction can be the same aspreviously disclosed in relation with FIG. 1, for example there may be aglue layer 71 between the top layer and the central layer, and anotherglue layer 72 between the central layer and the bottom layer. Thechannels are shown straight and parallel to the longitudinal axis, butcurved channels may be provided instead, in particular the channels maycomprise at least one pair of channels on each side of the longitudinalaxis and having a curvature which is concave towards the longitudinalaxis. i.e. like inverted brackets:) (.Having such curved channels mayprovide for better comfort when after the core has been loaded with afluid as the channels will generally follow the contour of the legs ofthe wearer.

Such absorbent cores may be produced as previously described in relationto FIG. 4, with the difference that the shielding plates are mobile tofollow the web of central layer passing beneath it. The SAP particlesexiting the sieving plate may pass through a shielding plate which ismounted on a rotating drum or a rotating belt. The rotating platecomprise a cut-out section through which the SAP particles can pass anddeposit onto the central layer, and full zones which prevent the SAPparticles from depositing onto the zones of the central layerimmediately beneath the full zones. Several shielding plates are mountedon each moving rotating drum or belt and the shield plates move at thesame speed as the web of high loft material underneath it so that thepattern of SAP distribution on the central layer generally correspondsto the pattern formed by the cut-out and full zones of the plates.However this technique may be difficult put in place to obtain precisedeposition at high speed.

The SAP particles may be instead deposited a SAP printing technology,which allows relatively precise deposition of SAP particles in desiredareas at relatively high speed. In particular the SAP printingtechnology as disclosed for example in US2006/24433 (Blessing),US2008/0312617 and US2010/0051166A1 (both to Hundorf et al.), and inparticular WO2012170798A1 (Jackels) may be used. As illustrated in FIG.8, this technique uses a printing roll 30 to deposit the SAP particlesonto a substrate (in this case the high loft central layer 43) disposedon a grid of a support (represented as vacuum box 10 but it may also bea circular rotating lay-on drum roll as taught in the references above).A feeder 25 feeds the SAP particles to the external surface of theprinting roll comprising at least one reservoir 32 and typically aplurality of reservoirs disposed on the circumference of the printingrolls. Each reservoir 32 comprises at least one raised strip 31, whichmay have a corresponding mating strip on the lay-on drum roll, and aplurality of grooves and/or cavities (not represented) between theraised strips having a void volume, for receiving the absorbentmaterial.

The SAP particles are fed from the feeder into the grooves or cavitiesof the reservoir except in the area of the raised strips. The particlesare then transferred onto the high loft nonwoven layer, for example by acombination of vacuum on the deposition side and overpressure on theprinting roll side at the meeting point. The absorbent material may alsobe deposited at different basis weight in selected areas by varying thevolumes or numbers of the grooves or cavities, so that, for examplethere is higher amount of absorbent material towards the front edge ofthe core than towards the back edge. This is disclosed in details in thereferences indicated above. The advantages of the SAP printing system isthat the channels may be clearly defined by the raised surfaces on theprinting roll, and may provide channels having a shape that is notstraight, for example curved as illustrated by the curved raised strips31 on FIG. 9.

The processes disclosed herein show the SAP particles deposited in twosteps, one step for each side of the central layer. However it is alsopossible that the SAP particles are only deposited once, on a singleside of the central layer, by removing one of the deposition devices.While in this case the SAP distribution may be less homogeneous in thethickness dimension of the central layer, this has the advantage ofsimplifying the making process of the core. It is also possible to firstattach the central layer 43 to the top (or bottom) layer 42 beforedepositing the first SAP particles.

Another process (not represented) for making a core of the invention isto punch or otherwise cut at least one piece of material in the centrallayer corresponding to the channels 26 before attaching it to the bottomand top layers. The SAP can then be homogenously deposited by anymethods on the punched or cut-off high loft central layer. The SAPparticles falling through the holes can then for example be recycled tothe feeder. The other processes described have however the advantagesthat the high loft material is present in the channels and thus providestability in the channel regions of the core.

Absorbent Core

The absorbent cores discussed previously comprise a single high loftnonwoven layer, however it is also possible that the absorbent corescomprise two (or more) high loft nonwoven layers between the top andbottom layers. The absorbent core thus may comprise a first centrallayer and a second central layer, each of which being a high loftfibrous nonwoven layer comprising superabsorbent polymer particlesblended between their fibers.

This is illustrated for example in FIG. 10 wherein the first centrallayer 431 and the second central layer 432 are shown sandwiched betweenthe top layer 41 and the bottom layer 42. Each and in particular both ofthe first and the second central layers may comprise one, two or morelongitudinally-extending channels 26, the channels being as indicatedbefore. In particular the channels may extend to the front and backedges of their central layer, or may be surrounded by a zone comprisingSAP. The channels in one central layer may generally correspond to thechannel in the other central layer. This is for example represented inFIG. 10. In the plan of the core (not shown), these channels in eachcentral layer may have the same configuration as those discussed in FIG.1 and FIG. 6 for example. The general indications made generally in theprevious sections also apply to an absorbent core having a dual centrallayer. Such absorbent cores may also comprise a wrapping layer aspreviously discussed.

As illustrated in FIG. 10 the channels in each central layer may beregistered and thus match each other but it is not excluded that thechannels of one layer may be completely or partially shiftedtransversally relative to the channels of the other layer. It is alsoconsidered than only one of the central layer may have channelsaccording to the invention. For example, only the first central layer431 closest to the top layer of the core may comprise the channels, andthe second central layer 432 may be absent of channels, in other wordsmay comprise SAP over its entire area. This may provide for a quickerabsorption of the fluid into the core. It is also possible that the highloft central layers have different basis weight, density and/or amountof AGM deposited. For example the permeability in the upper centrallayer may be enhanced by using a low basis weight high loft and softnessmay be enhanced in the bottom layer with a denser high loft material. Ofcourse other configurations are also possible. The two or more twocentral layers can be of equal dimensions in the plane of the core, butthey may also have different length and/or width. Two central layers ofunequal length could be beneficial to provide different amount of SAPalong the absorbent core, and made for example by adding a cut and slitunit on the second layer patch, and before combining it with the firstlayer.

It is also considered that the two high loft central layers may comprisedifferent sort of SAP, for example faster absorbing SAP (higher UPMvalue) in the first central layer 431 closer to the top layer and/or amore absorbing SAP (higher CRC) in the second central layer 432. Thechannels may have different shapes in each high loft central layers. Forthese reasons, an intermediate nonwoven or paper layer (not represented)can be placed between the two central layers to avoid that the SAPparticles deposited on the one central layer fall into the other centrallayer. Such intermediate layers may be attached to one or both of thecentral layers by any know means, for example by gluing.

Absorbent cores comprising a dual high loft nonwoven layers may be madeby a method adapted from one of the methods disclosed with reference toFIG. 4 and FIG. 8. Two separate high loft layer releasing cylinder 8 maybe provided to provide for the first and second high loft central layers431, 432, as shown in FIG. 11. As an alternative, a high loft web havinga double width may be used: such a large width roll can be cut afterrelease in machine direction in two halves providing for two streams ofhigh loft nonwoven material that are then separately deposited with SAPparticles. The two stream of high loft material 431, 432 may be thencombined separately with the top layer and bottom layer respectively,each having then SAP particles 60 deposited onto them through a suitableSAP deposition device. As discussed previously, each SAP depositiondevice may for example comprise a static or mobile shielding frame 22(as represented in FIG. 11) or a printing roll system as illustrated inFIGS. 8-9. It is also possible to deposit and blend the SAP into thefibers of only one of the first and second the central layer.

Absorbent Article

The absorbent cores may be incorporated into any kind of personalhygiene articles, which may be for example a baby diaper or a trainingpant. A schematic cross-sectional view showing some of the maincomponents of a taped diaper absorbent article 200 is illustrated inFIG. 12. In this Figure, the absorbent core of FIG. 10 (with a wrappinglayer 3) is shown, but this is of course not limiting and forillustration only. Absorbent articles typically comprise a wearer-facingfluid permeable topsheet 36 and a garment-facing liquid impermeablebacksheet 38 attached to each other along their perimeter. The absorbentcore is placed between these layers and may be attached directly andindirectly to these layers, typically by gluing or heat/pressurebonding.

The topsheet 36 is preferably compliant, soft-feeling, andnon-irritating to the wearer's skin. Further, at least a portion of thetopsheet is liquid permeable, permitting liquids to readily penetratethrough its thickness. A suitable topsheet may be manufactured from awide range of materials, such as porous foams, reticulated foams,apertured plastic films, or woven or nonwoven materials of naturalfibers (e.g., wood or cotton fibers), synthetic fibers or filaments(e.g., polyester or polypropylene or bicomponent PE/PP fibers ormixtures thereof), or a combination of natural and synthetic fibers. Ifthe topsheet includes fibers, the fibers may be spunbond, carded,wet-laid, meltblown, hydroentangled, or otherwise processed as is knownin the art, in particular spunbond PP nonwoven. Typical diaper topsheetshave a basis weight of from about 10 gsm to about 28 gsm, in particularbetween from about 12 gsm to about 18 gsm but other basis weights arepossible.

The backsheet 38 is typically impermeable to liquids (e.g. urine). Thebacksheet may for example be or comprise a thin plastic film such as athermoplastic film having a thickness of less than about 0.10 mm.Exemplary backsheet films include those manufactured by TredegarCorporation, based in Richmond, Va., and sold under the trade name CPC2film. Other suitable backsheet materials may include breathablematerials which permit vapors to escape from the article while stillpreventing exudates from passing through the backsheet. A covering lowbasis weight nonwoven may be attached to the external surface of thefilm to provide for a softer touch.

The absorbent articles may also comprise a liquid management layer 54(also called fluid acquisition or fluid distribution layer) directlyunder the topsheet 36. The function of such a layer is to rapidlyacquire the fluid from the topsheet away from the wearer-facing sideand/or to distribute over a larger area so it is more efficientlyabsorbed by the absorbent core. It is also possible that such a liquidmanagement layer may be placed between the backsheet and the absorbentcore. A further layer 4 may be present between the liquid management 54and the absorbent core 28. The further layer 4 may be another suchacquisition or distribution layer, or may be a tissue paper or low basisweight NW layer that provides an additional wrapping of the absorbentcore 28 to avoid SAP particles from escaping outside the core.

Absorbent articles such as diapers or training pants may typicallyfurther comprise components that improve the fit of the article aroundthe legs of the wearer, in particular barrier leg cuffs 32 and gasketingcuffs 34. The barrier leg cuffs may be formed by a piece of material,typically a nonwoven, which is partially bonded to the rest of thearticle and can be partially raised away and thus stand up from theplane defined by the topsheet. The barrier leg cuffs are typicallydelimited by a proximal edge joined to the rest of the article,typically the topsheet and/or the backsheet, and a free terminal edgeintended to contact and form a seal with the wearer's skin. The standingup portion of the cuffs typically comprise an elastic element, forexample one or a plurality of elastic strands 35. The barrier leg cuffsprovide improved containment of liquids and other body exudatesapproximately at the junction of the torso and legs of the wearer.

In addition to the barrier leg cuffs, the article may comprise gasketingcuffs 34, which are formed in the same plane as the chassis of theabsorbent article, in particular which may be at least partiallyenclosed between the topsheet or the barrier leg cuffs and thebacksheet, and may be placed laterally outwardly relative to theupstanding barrier leg cuffs. The gasketing cuffs can provide a betterseal around the thighs of the wearer. Usually each gasketing leg cuffwill comprise one or more elastic string or elastic element 33 comprisedin the chassis of the diaper for example between the topsheet andbacksheet in the area of the leg openings.

The absorbent articles may also include other typical components foundin diapers, training pants or adult incontinence products (and notfurther represented). A releasable fastening system for taped diapersmay be provided to provide lateral tensions about the circumference ofthe absorbent article to hold the absorbent article on the wearer. Thisfastening system is not necessary for training pants since the waistregion of these articles is already bonded. The fastening system usuallycomprises a fastener such as tape tabs, hook and loop fasteningcomponents, interlocking fasteners such as tabs & slots, buckles,buttons, snaps, and/or hermaphroditic fastening components, although anyother known fastening means are generally acceptable. A landing zone isnormally provided on the front waist region of the article for thefastener to be releasably attached.

The absorbent article may comprise front ears and back ears as is knownin the art. The ears can be integral part of the chassis, for exampleformed from the topsheet and/or backsheet as side panel. Alternatively,they may be separate elements attached by gluing and/or heat embossing.The back ears are advantageously stretchable to facilitate theattachment of the tabs on the landing zone and maintain the tapeddiapers in place around the wearer's waist. The front ears may also beelastic or extensible to provide a more comfortable and contouring fitby initially conformably fitting the absorbent article to the wearer andsustaining this fit throughout the time of wear well past when absorbentarticle has been loaded with exudates since the elasticized ears allowthe sides of the absorbent article to expand and contract.

Relations Between the Layers and Components

Typically, adjacent layers will be joined together using conventionalbonding method such as adhesive coating via slot coating or spraying onthe whole or part of the surface of the layer, or thermo-bonding, orpressure bonding or combinations thereof. The bonding between componentsis for clarity and readability not represented in the majority ofFigures, in particular FIG. 12. Adjacent layers of the article should beconsidered to be attached to another unless specifically mentionedotherwise. For example the backsheet and the bottom layer of theabsorbent core may be typically glued together. The adhesives used maybe any standard hotmelt glue as known in the art.

Packaging

The absorbent articles may be packaged in any type of conventionalpackaging. The absorbent articles may be in particular compressed whenpackaged to save space. In particular the package may comprise aplurality of the absorbent articles, wherein the package has an in-bagstack height of less than about 80 mm, according to the In-Bag StackHeight Test as described in U.S. Pat. No. 8,585,666 B2 (Weismann),incorporated herein by reference. Alternatively, packages of theabsorbent articles of the present disclosure may have an in-bag stackheight of from about 72 mm to about 80 mm or from about 74 mm to about78 mm, specifically reciting all 0.5 mm increments within the specifiedranges and all ranges formed therein or thereby, according to theIn-Back Stack Height Test.

Test Procedures

The values indicated herein are measured according to the methodsindicated herein below, unless specified otherwise. All measurements areperformed at 21° C.±2° C. and 50%±20% RH, unless specified otherwise.All samples should be kept at least 24 hours in these conditions toequilibrate before conducting the tests, unless indicated otherwise. Allmeasurements should be reproduced on at least 4 samples and the averagevalue obtained indicated, unless otherwise indicated.

Centrifuge Retention Capacity (CRC)

The CRC measures the liquid absorbed by the superabsorbent polymerparticles for free swelling in excess liquid. The CRC is measuredaccording to EDANA method WSP 241.2-05.

Urine Permeability Measurement (UPM) Test Method

This method determines the permeability of a swollen hydrogel layer1318.

FIG. 13 shows a permeability measurement system 1000 set-up with theconstant hydrostatic head reservoir 1014, open-ended tube for airadmittance 1010, stoppered vent for refilling 1012, laboratory jack1016, delivery tube 1018, stopcock 1020, ring stand support 1022,receiving vessel 1024, balance 1026 and piston/cylinder assembly 1028.

FIG. 14 shows the piston/cylinder assembly 1028 comprising a metalweight 1112, piston shaft 1114, piston head 1118, lid 1116, and cylinder1120. The cylinder 1120 is made of transparent polycarbonate (e.g.,Lexan®) and has an inner diameter p of 6.00 cm (area=28.27 cm2) withinner cylinder walls 1150 which are smooth. The bottom 1148 of thecylinder 1120 is faced with a US. Standard 400 mesh stainless-steelscreen cloth (not shown) that is bi-axially stretched to tautness priorto attachment to the bottom 1148 of the cylinder 1120. The piston shaft1114 is made of transparent polycarbonate (e.g., LEXAN®) and has anoverall length q of approximately 127 mm. A middle portion 1126 of thepiston shaft 1114 has a diameter r of 21.15 mm. An upper portion 1128 ofthe piston shaft 1114 has a diameter s of 15.8 mm, forming a shoulder1124. A lower portion 1146 of the piston shaft 1114 has a diameter t ofapproximately ⅝ inch and is threaded to screw firmly into the centerhole 1218 (see FIG. 15) of the piston head 1118. The piston head 1118 isperforated, made of transparent polycarbonate (e.g., LEXAN®), and isalso screened with a stretched US. Standard 400 mesh stainless-steelscreen cloth (not shown). The weight 1112 is stainless steel, has acenter bore 1130, slides onto the upper portion 1128 of piston shaft1114 and rests on the shoulder 1124. The combined weight of the pistonhead 1118, piston shaft 1114 and weight 1112 is 596 g (±6 g), whichcorresponds to 0.30 psi (2.07 kPa) over the area of the cylinder 1120.The combined weight may be adjusted by drilling a blind hole down acentral axis 1132 of the piston shaft 1114 to remove material and/orprovide a cavity to add weight. The cylinder lid 1116 has a first lidopening 1134 in its center for vertically aligning the piston shaft 1114and a second lid opening 1136 near the edge 1138 for introducing fluidfrom the constant hydrostatic head reservoir 1014 into the cylinder1120.

A first linear index mark (not shown) is scribed radially along theupper surface 1152 of the weight 1112, the first linear index mark beingtransverse to the central axis 1132 of the piston shaft 1114. Acorresponding second linear index mark (not shown) is scribed radiallyalong the top surface 1160 of the piston shaft 1114, the second linearindex mark being transverse to the central axis 1132 of the piston shaft1114. A corresponding third linear index mark (not shown) is scribedalong the middle portion 1126 of the piston shaft 1114, the third linearindex mark being parallel with the central axis 1132 of the piston shaft1114. A corresponding fourth linear index mark (not shown) is scribedradially along the upper surface 1140 of the cylinder lid 1116, thefourth linear index mark being transverse to the central axis 1132 ofthe piston shaft 1114. Further, a corresponding fifth linear index mark(not shown) is scribed along a lip 1154 of the cylinder lid 1116, thefifth linear index mark being parallel with the central axis 1132 of thepiston shaft 1114. A corresponding sixth linear index mark (not shown)is scribed along the outer cylinder wall 1142, the sixth linear indexmark being parallel with the central axis 1132 of the piston shaft 1114.Alignment of the first, second, third, fourth, fifth, and sixth linearindex marks allows for the weight 1112, piston shaft 1114, cylinder lid1116, and cylinder 1120 to be re-positioned with the same orientationrelative to one another for each measurement.

The cylinder 1120 specification details are:

-   -   Outer diameter u of the Cylinder 1120: 70.35 mm    -   Inner diameter p of the Cylinder 1120: 60.0 mm    -   Height v of the Cylinder 1120: 60.5 mm

The cylinder lid 1116 specification details are:

-   -   Outer diameter w of cylinder lid 1116: 76.05 mm    -   Inner diameter x of cylinder lid 1116: 70.5 mm    -   Thickness y of cylinder lid 1116 including lip 1154: 12.7 mm    -   Thickness z of cylinder lid 1116 without lip 1154: 6.35 mm    -   Diameter a of first lid opening 1134: 22.25 mm    -   Diameter b of second lid opening 1136: 12.7 mm    -   Distance between centers of first and second lid openings 1134        and 1136: 23.5 mm

The weight 1112 specification details are:

-   -   Outer diameter c: 50.0 mm    -   Diameter d of center bore 1130: 16.0 mm    -   Height e: 39.0 mm

The piston head 1118 specification details are

-   -   Diameter f: 59.7 mm    -   Height g: 16.5 mm    -   Outer holes 1214 (14 total) with a 9.65 mm diameter h, outer        holes 1214 equally spaced with centers being 47.8 mm from the        center of center hole 1218    -   Inner holes 1216 (7 total) with a 9.65 mm diameter i, inner        holes 1216 equally spaced with centers being 26.7 mm from the        center of center hole 1218    -   Center hole 1218 has a diameter j of ⅝ inches and is threaded to        accept a lower portion 1146 of piston shaft 1114.

Prior to use, the stainless steel screens (not shown) of the piston head1118 and cylinder 1120 should be inspected for clogging, holes orover-stretching and replaced when necessary. A urine permeabilitymeasurement apparatus with damaged screen can deliver erroneous UPMresults, and must not be used until the screen has been replaced.

A 5.00 cm mark 1156 is scribed on the cylinder 1120 at a height k of5.00 cm (±0.05 cm) above the screen (not shown) attached to the bottom1148 of the cylinder 1120. This marks the fluid level to be maintainedduring the analysis. Maintenance of correct and constant fluid level(hydrostatic pressure) is critical for measurement accuracy.

A constant hydrostatic head reservoir 1014 is used to deliver saltsolution 1032 to the cylinder 1120 and to maintain the level of saltsolution 1032 at a height k of 5.00 cm above the screen (not shown)attached to the bottom 1148 of the cylinder 1120. The bottom 1034 of theair-intake tube 1010 is positioned so as to maintain the salt solution1032 level in the cylinder 1120 at the required 5.00 cm height k duringthe measurement, i.e., bottom 1034 of the air tube 1010 is inapproximately same plane 1038 as the 5.00 cm mark 1156 on the cylinder1120 as it sits on the support screen (not shown) on the ring stand 1040above the receiving vessel 1024. Proper height alignment of theair-intake tube 1010 and the 5.00 cm mark 1156 on the cylinder 1120 iscritical to the analysis. A suitable reservoir 1014 consists of a jar1030 containing: a horizontally oriented L-shaped delivery tube 1018 forfluid delivery, a vertically oriented open-ended tube 1010 for admittingair at a fixed height within the constant hydrostatic head reservoir1014, and a stoppered vent 1012 for re-filling the constant hydrostatichead reservoir 1014. Tube 1010 has an internal diameter of 12.5 mm±0.5mm. The delivery tube 1018, positioned near the bottom 1042 of theconstant hydrostatic head reservoir 1014, contains a stopcock 1020 forstarting/stopping the delivery of salt solution 1032. The outlet 1044 ofthe delivery tube 1018 is dimensioned to be inserted through the secondlid opening 1136 in the cylinder lid 1116, with its end positioned belowthe surface of the salt solution 1032 in the cylinder 1120 (after the5.00 cm height of the salt solution 1032 is attained in the cylinder1120). The air-intake tube 1010 is held in place with an o-ring collar(not shown). The constant hydrostatic head reservoir 1014 can bepositioned on a laboratory jack 1016 in order to adjust its heightrelative to that of the cylinder 1120. The components of the constanthydrostatic head reservoir 1014 are sized so as to rapidly fill thecylinder 1120 to the required height (i.e., hydrostatic head) andmaintain this height for the duration of the measurement. The constanthydrostatic head reservoir 1014 must be capable of delivering saltsolution 1032 at a flow rate of at least 3 g/sec for at least 10minutes.

The piston/cylinder assembly 1028 is positioned on a 16 mesh rigidstainless steel support screen (not shown) (or equivalent) which issupported on a ring stand 1040 or suitable alternative rigid stand. Thissupport screen (not shown) is sufficiently permeable so as to not impedesalt solution 1032 flow and rigid enough to support the stainless steelmesh cloth (not shown) preventing stretching. The support screen (notshown) should be flat and level to avoid tilting the piston/cylinderassembly 1028 during the test. The salt solution 1032 passing throughthe support screen (not shown) is collected in a receiving vessel 1024,positioned below (but not supporting) the support screen (not shown).The receiving vessel 1024 is positioned on the balance 1026 which isaccurate to at least 0.01 g. The digital output of the balance 1026 isconnected to a computerized data acquisition system (not shown).

Preparation of Reagents (not Illustrated)

Jayco Synthetic Urine (JSU) 1312 (see FIG. 16) is used for a swellingphase (see UPM Procedure below) and 0.118 M Sodium Chloride (NaCl)Solution is used for a flow phase (see UPM Procedure below). Thefollowing preparations are referred to a standard 1 liter volume. Forpreparation of volumes other than 1 liter, all quantities are scaledaccordingly.

JSU: A 1 L volumetric flask is filled with distilled water to 80% of itsvolume, and a magnetic stir bar is placed in the flask. Separately,using a weighing paper or beaker the following amounts of dryingredients are weighed to within ±0.01 g using an analytical balanceand are added quantitatively to the volumetric flask in the same orderas listed below. The solution is stirred on a suitable stir plate untilall the solids are dissolved, the stir bar is removed, and the solutiondiluted to 1 L volume with distilled water. A stir bar is againinserted, and the solution stirred on a stirring plate for a few minutesmore.

Quantities of salts to make 1 liter of Jayco Synthetic Urine:

-   -   Potassium Chloride (KCl) 2.00 g    -   Sodium Sulfate (Na₂SO4) 2.00 g    -   Ammonium dihydrogen phosphate (NH₄H₂PO₄) 0.85 g    -   Ammonium phosphate, dibasic ((NH₄)₂HPO₄) 0.15 g    -   Calcium Chloride (CaCl₂) 0.19 g—[or hydrated calcium chloride        (CaCl₂.2H₂O) 0.25 g]    -   Magnesium chloride (MgCl₂) 0.23 g—[or hydrated magnesium        chloride (MgCl₂.6H₂O) 0.50 g]

To make the preparation faster, each salt is completely dissolved beforeadding the next one. Jayco synthetic urine may be stored in a cleanglass container for 2 weeks. The solution should not be used if itbecomes cloudy. Shelf life in a clean plastic container is 10 days.

0.118 M Sodium Chloride (NaCl) Solution: 0.118 M Sodium Chloride is usedas salt solution 1032. Using a weighing paper or beaker 6.90 g (±0.01 g)of sodium chloride is weighed and quantitatively transferred into a 1 Lvolumetric flask; and the flask is filled to volume with distilledwater. A stir bar is added and the solution is mixed on a stirring plateuntil all the solids are dissolved.

Test Preparation

Using a solid reference cylinder weight (not shown) (40 mm diameter; 140mm height), a caliper gauge (not shown) (e.g., Mitotoyo Digimatic HeightGage) is set to read zero. This operation is conveniently performed on asmooth and level bench top 1046. The piston/cylinder assembly 1028without superabsorbent polymer particles is positioned under the calipergauge (not shown) and a reading, L₁, is recorded to the nearest 0.01 mm.

The constant hydrostatic head reservoir 1014 is filled with saltsolution 1032. The bottom 1034 of the air-intake tube 1010 is positionedso as to maintain the top part (not shown) of the liquid meniscus (notshown) in the cylinder 1120 at the 5.00 cm mark 1156 during themeasurement. Proper height alignment of the air-intake tube 1010 at the5.00 cm mark 1156 on the cylinder 1120 is critical to the analysis.

The receiving vessel 1024 is placed on the balance 1026 and the digitaloutput of the balance 1026 is connected to a computerized dataacquisition system (not shown). The ring stand 1040 with a 16 mesh rigidstainless steel support screen (not shown) is positioned above thereceiving vessel 1024. The 16 mesh screen (not shown) should besufficiently rigid to support the piston/cylinder assembly 1028 duringthe measurement. The support screen (not shown) must be flat and level.

UPM Procedure

The measurements should be preferably made on the superabsorbent polymerparticles raw material before it is converted into an absorbent core. Ifthis is not possible, a sufficient SAP sample should be obtained fromthe finished absorbent cores by manually extracting the SAP particlesfrom the central layer.

The moisture content of the superabsorbent polymer particles is measuredon a first sample according to the EDANA Moisture Content Test MethodWSP 230.2.R3 (12) (“Superabsorbent materials—Polyacrylate superabsorbentpowders—Moisture Content—weight loss upon heating”). Another sample of1.5 g (±0.05 g) of superabsorbent polymer particles is weighed onto asuitable weighing paper or weighing aid using an analytical balance. Ifthe moisture content of the superabsorbent polymer particles is greaterthan 5%, then the superabsorbent polymer particles weight should becorrected for moisture (i.e., in that particular case the addedsuperabsorbent polymer particles should be 1.5 g on a dry-weight basis).

The empty cylinder 1120 is placed on a level benchtop 1046 and thesuperabsorbent polymer particles are quantitatively transferred into thecylinder 1120. The superabsorbent polymer particles are evenly dispersedon the screen (not shown) attached to the bottom 1148 of the cylinder1120 by gently shaking, rotating, and/or tapping the cylinder 1120. Itis important to have an even distribution of particles on the screen(not shown) attached to the bottom 1148 of the cylinder 1120 to obtainthe highest precision result. After the superabsorbent polymer particleshave been evenly distributed on the screen (not shown) attached to thebottom 1148 of the cylinder 1120 particles must not adhere to the innercylinder walls 1150. The piston shaft 1114 is inserted through the firstlid opening 1134, with the lip 1154 of the lid 1116 facing towards thepiston head 1118. The piston head 1118 is carefully inserted into thecylinder 1120 to a depth of a few centimeters. The lid 1116 is thenplaced onto the upper rim 1144 of the cylinder 1120 while taking care tokeep the piston head 1118 away from the superabsorbent polymerparticles. The lid 1116 and piston shaft 1126 are then carefully rotatedso as to align the third, fourth, fifth, and sixth linear index marksare then aligned. The piston head 1118 (via the piston shaft 1114) isthen gently lowered to rest on the dry superabsorbent polymer particles.The weight 1112 is positioned on the upper portion 1128 of the pistonshaft 1114 so that it rests on the shoulder 1124 such that the first andsecond linear index marks are aligned. Proper seating of the lid 1116prevents binding and assures an even distribution of the weight on thehydrogel layer 1318.

Swelling Phase: An 8 cm diameter fritted disc (7 mm thick; e.g.Chemglass Inc. #CG 201-51, coarse porosity) 1310 is saturated by addingexcess JSU 1312 to the fritted disc 1310 until the fritted disc 1310 issaturated. The saturated fritted disc 1310 is placed in a wideflat-bottomed Petri dish 1314 and JSU 1312 is added until it reaches thetop surface 1316 of the fritted disc 1310. The JSU height must notexceed the height of the fitted disc 1310.

The screen (not shown) attached to the bottom 1148 of the cylinder 1120is easily stretched. To prevent stretching, a sideways pressure isapplied on the piston shaft 1114, just above the lid 1116, with theindex finger while grasping the cylinder 1120 of the piston/cylinderassembly 1028. This “locks” the piston shaft 1114 in place against thelid 1116 so that the piston/cylinder assembly 1028 can be lifted withoutundue force being exerted on the screen (not shown).

The entire piston/cylinder assembly 1028 is lifted in this fashion andplaced on the fritted disc 1310 in the Petri dish 1314. JSU 1312 fromthe Petri dish 1314 passes through the fritted disc 1310 and is absorbedby the superabsorbent polymer particles (not shown) to form a hydrogellayer 1318. The JSU 1312 available in the Petri dish 1314 should beenough for all the swelling phase. If needed, more JSU 1312 may be addedto the Petri dish 1314 during the hydration period to keep the JSU 1312level at the top surface 1316 of the fritted disc 1310. After a periodof 60 minutes, the piston/cylinder assembly 1028 is removed from thefritted disc 1310, taking care to lock the piston shaft 1114 against thelid 1116 as described above and ensure the hydrogel layer 1318 does notlose JSU 1312 or take in air during this procedure. The piston/cylinderassembly 1028 is placed under the caliper gauge (not shown) and areading, L₂, is recorded to the nearest 0.01 mm. If the reading changeswith time, only the initial value is recorded. The thickness of thehydrogel layer 1318, L₀ is determined from L₂−L₁ to the nearest 0.1 mm.

The piston/cylinder assembly 1028 is transferred to the support screen(not shown) attached to the ring support stand 1040 taking care to lockthe piston shaft 1114 in place against the lid 1116. The constanthydrostatic head reservoir 1014 is positioned such that the deliverytube 1018 is placed through the second lid opening 1136. The measurementis initiated in the following sequence:

-   -   a) The stopcock 1020 of the constant hydrostatic head reservoir        1014 is opened to permit the salt solution 1032 to reach the        5.00 cm mark 1156 on the cylinder 1120. This salt solution 1032        level should be obtained within 10 seconds of opening the        stopcock 1020.    -   b) Once 5.00 cm of salt solution 1032 is attained, the data        collection program is initiated.

With the aid of a computer (not shown) attached to the balance 1026, thequantity of salt solution 1032 passing through the hydrogel layer 1318is recorded at intervals of 20 seconds for a time period of 10 minutes.At the end of 10 minutes, the stopcock 1020 on the constant hydrostatichead reservoir 1014 is closed.

The data from 60 seconds to the end of the experiment are used in theUPM calculation. The data collected prior to 60 seconds are not includedin the calculation. The flow rate F_(s) (in g/s) is the slope of alinear least-squares fit to a graph of the weight of salt solution 1032collected (in grams) as a function of time (in seconds) from 60 secondsto 600 seconds.

The Urine Permeability Measurement (Q) of the hydrogel layer 1318 iscalculated using the following equation:

Q=[F _(g) ×L ₀]/[ρ×A×ΔP],

where F_(g) is the flow rate in g/sec determined from regressionanalysis of the flow rate results, L₀ is the initial thickness of thehydrogel layer 1318 in cm, ρ is the density of the salt solution 1032 ingm/cm³. A (from the equation above) is the area of the hydrogel layer1318 in cm², ΔP is the hydrostatic pressure in dyne/cm², and the UrinePermeability Measurement, Q, is in units of cm³ sec/gm. The average ofthree determinations should be reported.

High Loft Nonwoven Layer Thickness and Density Measurement Method

This method is used to measure the thickness of a high loft fibrousnonwoven central layer in a standardized manner. The density can then becalculated from the thickness. Unless otherwise mentioned, the thicknessand density are indicated for the high loft material in the absence ofSAP particles. The measurement should preferably be made on the highloft material before it was converted into an absorbent core and thusfree of SAP. If the starting material is not available, the high loftcentral layer can be obtained by carefully extracting it from anabsorbent core, and removing the majority of SAP particles for exampleby careful shaking or suction. A freeze spray may be used to separatethe central layer from the other layers. The samples should be kept atleast 24 hours at 21° C.±2° C. and 50%±20% RH to equilibrate, inparticular if they have been previously compressed.

Equipment: Mitutoyo manual caliper gauge with a resolution of 0.01 mm,or equivalent instrument.

Contact Foot: Flat circular foot with a diameter of 17.0 mm (±0.2 mm). Acircular weight may be applied to the foot (e.g., a weight with a slotto facilitate application around the instrument shaft) to achieve thetarget weight. The total weight of foot and added weight (includingshaft) is selected to provide 4.14 kPa of pressure to the sample.

The caliper gauge is mounted with the lower surface of the contact footin an horizontal plane so that the lower surface of the contact footcontacts the center of the flat horizontal upper surface of a base plateapproximately 20×25 cm. The gauge is set to read zero with the contactfoot resting on the base plate.

Ruler: Calibrated metal ruler graduated in mm.

Stopwatch: Accuracy 1 second.

Sample preparation: The central layer is conditioned at least 24 hoursas indicated above. Measurement procedure: The layer is laid flat withthe bottom side, i.e. the side intended to be placed towards thebacksheet in the finished article facing down. The point of measurement,i.e. the middle of the sample, is carefully drawn on the top side of thelayer, taking care not to compress or deform the layer. In the unlikelycase that the high loft nonwoven layer is not homogeneous in thetransversal direction or longitudinal direction, the values are measuredin the center of a sample corresponding to the center of an absorbentcore that would be made from the sample. Typically however the high loftfibrous nonwoven layer is homogeneous.

The contact foot of the caliper gauge is raised and the central layer isplaced flat on the base plate of the caliper gauge with the top side ofthe core up so that when lowered, the center of the foot is on themarked measuring point.

The foot is gently lowered onto the sample and released (ensurecalibration to “0” prior to the start of the measurement). The calipervalue is read to the nearest 0.01 mm, 10 seconds after the foot isreleased.

The procedure is repeated for each measuring point. Ten samples aremeasured in this manner for a given material and the average caliper iscalculated and reported with an accuracy of one tenth mm. The basisweight of each sample is calculated by dividing the weight of eachsample by their area.

The density, in g/cc, is calculated by dividing the basis weight (ing/cm²) of the material by the thickness (in cm).

Misc.

Dimensions and values disclosed herein are not to be understood as beingstrictly limited to the exact numerical values recited. Instead, unlessotherwise specified, each such dimension is intended to mean both therecited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm”.

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An absorbent core for use in an absorbentarticle, the absorbent core extending in a transversal direction and alongitudinal direction, the absorbent core comprising: a fluid-permeabletop layer; a bottom layer; a central layer sandwiched between the toplayer and the bottom layer, the central layer having a front edge, aback edge and two longitudinally extending side edges, wherein thecentral layer is a high loft fibrous nonwoven layer comprising syntheticfibers; and superabsorbent polymer particles blended with the syntheticfibers of the central layer; wherein the central layer has a density ofabout 0.200 g/cc or less, and wherein the central layer comprises alongitudinally-extending channel substantially free of superabsorbentpolymer particles.
 2. The absorbent core of claim 1, wherein at leastone of the top layer, the bottom layer, and the central layer comprisesa carded nonwoven.
 3. The absorbent core of claim 1, wherein thesuperabsorbent polymer particles have a UPM of about 30×10⁻⁷ cm³·s/g orless.
 4. The absorbent core of claim 1, wherein at least one of the toplayer and the bottom layer is attached to the central layer by gluing.5. The absorbent core of claim 1, wherein at least one of the top layerand the bottom layer are bonded to the central layer in the channels byat least one of gluing, mechanical bonding, ultrasonic bonding, pressurebonding, and heat bonding.
 6. The absorbent core of claim 1, wherein thechannel is spaced away from the longitudinally extending side edges ofthe core.
 7. The absorbent core of claim 1, comprising a nonwovenwrapping layer configured to wrap at least one of the top layer, thebottom layer, and the central layer.
 8. The absorbent core of claim 7,wherein the wrapping layer completely covers one of the bottom layer orthe top layer and forms a C-wrap around the longitudinally extendingside edges of the central layer to at least partially cover the other ofthe top layer or the bottom layer.
 9. The absorbent core of claim 1,wherein the channel is completely surrounded by at least one zone of thecentral layer comprising superabsorbent polymer particles.
 10. Theabsorbent core of claim 1, wherein the channel extends longitudinallyfrom the front edge to the back edge of the central layer.
 11. Theabsorbent core of claim 1, comprising a least a pair of channelssymmetrically disposed along a longitudinal axis of the core.
 12. Theabsorbent core of claim 11, wherein the channels are curved.
 13. Theabsorbent core of claim 1, wherein the central layer is a spunlaidnonwoven of synthetic fibers and is free of cellulose fibers.
 14. Theabsorbent core of claim 1, comprising a first central layer and a secondcentral layer between the top layer and the bottom layer, wherein atleast one of the first central layer and the second central layer is acentral layer according to claim
 1. 15. An absorbent article, theabsorbent article comprising: absorbent core extending in a transversaldirection and a longitudinal direction, the absorbent core comprising: afluid-permeable top layer; a bottom layer; a central layer sandwichedbetween the top layer and the bottom layer, the central layer having afront edge, a back edge and two longitudinally extending side edges,wherein the central layer is a high loft fibrous nonwoven layercomprising synthetic fibers; and superabsorbent polymer particlesblended with the synthetic fibers of the central layer, wherein thecentral layer has a density of about 0.200 g/cc or less, and wherein thecentral layer comprises a longitudinally-extending channel substantiallyfree of superabsorbent polymer particles.
 16. The absorbent article ofclaim 15, comprising a topsheet and a backsheet.
 17. The absorbentarticle of claim 16, comprising at least one of an acquisition layer ora distribution layer between the absorbent core and topsheet.
 18. Theabsorbent article of claim 15, wherein the synthetic fibers comprise atleast one of polypropylene fibers, polyamide fibers, and polyethyleneterephthalate fibers.
 19. The absorbent article of claim 15, wherein thecentral layer comprises a spunmelt nonwoven.
 20. A continuous processfor making absorbent cores, the process comprising: providing a bottomlayer; providing a fluid permeable top layer; providing a central layer,wherein the central layer is a high loft nonwoven layer comprisingsynthetic fibers, wherein the central layer comprises a channel;depositing superabsorbent polymer particles on a first side of thecentral layer so that the superabsorbent polymer particles are blendedwith the synthetic fibers of the central layer, with the exception ofthe channel which remain substantially free of superabsorbent polymerparticles; attaching the bottom layer to a first side of the centrallayer; and attaching the top layer to the second side of the centrallayer.